We propose to study the interaction of human erythrocytes, antibody and complement with particular reference to paroxysmal nocturnal hemoglobinuria (PNH) and auto-immune hemolytic anemia (AIHA). In PNH we plan to study the mechanisms of hemolysis in the sucrose hemolysis reaction and the acid hemolysis reaction. We also plan to investigate the mechanisms for hemolysis of artificial "PNH-like" cells in these same systems. In AIHA we plan to study mechanisms responsible for erythrocyte coating with immunoglobulins and complement components. Emphasis will be given to studies of mechanisms of erythrocyte complement coating by auto-antibodies as well as studies of antigen specificity of auto- antibodies.